This is a proposal to develop a retinal model of neurodegeneration that will ultimately enable much more rapid and efficient evaluation of chemical modifiers of disease than is currently possible. We are carrying out proof-of-concept experiments using the huntingtin (Htt) protein, which causes Huntington disease when it contains an elongated tract of glutamines. The significance of this work is high, because if we are successful we will show that it is possible to isolate a discrete portion of the CNS for chemical and genetic studies, using anatomy, physiology, and function. This could help bridge cellular studies of neurodegeneration, which can rapidly generate much data, with whole animal studies, which are expensive and time consuming. The retinal model allows independent measurement of function in each eye, enabling internal controls within an animal that vastly improve statistical power. In preliminary work, we have shown that it is possible to detect retinal degeneration in the R6/2 mouse model of HD. We have further demonstrated that this is associated with progressive loss of function in tests of retinal physiology (electroretinography). We have shown that it is possible to deliver a disease-modifying compound in tiny amounts using liposome-mediated drug delivery, and to observe a beneficial effect on retinal physiology. We have also developed a behavior assay that lets us independently measure vision in the right vs. left eye of an unrestrained mouse. Finally, we have shown that it is possible to transduce large numbers of retinal neurons after a single injection of a modified adeno-associated virus. This work puts us in an excellent position to test whether we can build a model of retinal degeneration based on expression of various Htt proteins with mutations of broad interest to the HD field. Aim 1: Characterize viral transduction of Htt proteins within the retina. We will use AAV2 to express various forms of Htt and determine their effects on retinal neurons over time. Aim 2: Use ERG to measure effects on retinal physiology and compare mutants. We will use electroretinography to measure effects of various Htt proteins on retinal physiology. Aim 3. Use optomotry to measure effects on retinal neuron function and compare mutants. We will use a specialized behavior assay to measure the effects of various Htt proteins on visual function. The work is based on the use of recombinant adeno-associated virus, micro-injection of this virus into the intraocular space of wild-type mice, and the determination of the consequences of virus-mediated Htt gene expression within the eye. We will also use state-of-the-art techniques to monitor retinal pathology, physiology, and function. If successful, this work will set the stage for much more rapid in vivo analyses of chemical and genetic modifiers of neurodegeneration. This could have an enormous impact on human health, since neurodegenerative disease is one of the single biggest health problems faced by the United States.